December 2004

On December 25, the Cassini mission that arrived at Saturn a couple of months ago, will release the Huygens probe which will land on the moon Titan; Saturn's largest moon. This will be one of the Cassini mission milestones.

Titan was discovered in 1655, by Dutch astronomer Christiaan Huygens (April 14, 1629 - July 8, 1695). Christiaan came from an important Dutch family. His father was the famed (by the Dutch at least) Constantijn Huygens who was a philosopher but most importantly a diplomat. Christiaan received a private education at home by tutors until he was 16 years old, after which he studied Law and Mathematics at the University of Leiden.

At a certain point, Christiaan turned his attention to lens grinding and polishing and soon discovered a way to improve this process. He was therefore able to build superior telescopes that could resolve objects in the heavens not seen before. When he set out to study Saturn he indeed spotted the first moon: Titan. He was also able to make a detailed study on the shape of Saturn's rings.

Another very important invention Huygens made was the pendulum clock. Making observations and scientific research requires precise timekeeping, which was unavailable at the time. The pendulum clock was a major improvement, making it finally possible to measure longitude on board ships traveling the globe.

Just like Cassini, Huygens was a man that had a great influence on our history and both made incredible inventions. What a great way to honor these two great men by naming the Cassini-Huygens mission after them.

At this point we still do not know what the Huygens probe will find on Titan. We do not even know if it will land on solid surface or if it will splash down in some liquid. The Huygens probe has been built to be able to do both and to take pictures of its surroundings. Unfortunately the probe will not live very long at the most a couple of hours before it stops sending data. For more information on the Cassini-Huygens mission please visit the home page of the mission to Saturn and Titan.

Special Event

As you can see on the calendar; this December is quite a busy month. We won't detail everything that happens this month, but we will highlight some of the more remarkable events: the occultation of Jupiter on December the 7th, and the alignment of the planets.

Last October we had a spectacular Lunar Eclipse, where the moon travels through the Earth's shadow, or said differently: where the Earth traveled between the Sun and the Moon. If we would have been on the moon we would have seen a solar eclipse! This time something similar happens, where the Moon will stand between the Earth and Jupiter. From Earth, the moon will obscure Jupiter and some time later Jupiter will reappear from behind the Moon's limb. This reappearance should be quite spectacular because the moon will not be full and Jupiter will reappear from the dark crescent of the Moon. You will have to get up early for this though because the moon won't rise till 2 am right around the same time the 'show' will start for observers in Central Texas. Less then half an hour later Jupiter will be visible again.

Less spectacular, but still noteworthy is the alignment of all the major Planets. As you can read in this month 'The Planets' section (see above) all planets are visible and easily spotted later in the month. From the 10th through the 13th while not all of them are visible yet, they do appear in the sky in the same order as their respective distances from the Sun! The order is of course: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and even Pluto appears in the right spot. For Uranus and Neptune you will need a telescope. Mercury & Pluto are too close to the Sun and as a result they are impossible to see.

Although scientifically lineups like these are meaningless, they are very rare. A lineup like this will not happen again for another 400 years!

November 2004

The top Image is the outside of the Eise Eisinga museum in Franeker, The Netherlands. The lower picture is a portion of the machinery to keep the planetarium going. (images courtesy Eise Eisinga Planetarium)

Last month we observed a lunar eclipse, and this month we have the chance to see the conjunction of Venus and Jupiter. These two events have something in common: they both can cause fear with people that do not understand what is happening.

A very good example is the conjunction of four planets in the year 1774. Some people were afraid that the planets would actually run into each other, which would lead to the end of the world! This viewpoint was even published by a newspaper in the Netherlands.

Thankfully, a local wool-comber in the Dutch town of Franeker thought this was so outrageous that he decided to set these people straight. He built a scale model of the solar system (a planetarium, in other words) right in his living room. His name was Eise Eisinga. He built the entire contraption from wood; all of it by hand. Eventually, he indeed had a working scale model in his living room. It adequately showed the movement of the planets and moon. He was able to show and explain to people how our solar system works. By this wonderful visual resource he created, he was able to demonstrate to others that we do not need to be afraid that the planets will ever run into each other.

During the construction of all this, his wife had to put up with a lot. Their house was rather small, and the only place where the required pendulum could go was right in the middle of where their bed was at. After some re-design efforts, Eise was able to move the clockwork mechanism off to one side of their bedroom. This allowed the bedroom to be useable again and probably went a long way to making amends with his wife.

Another amazing thing about Eise’s planetarium is that it is still working to this day! The entire house has been turned into a museum. It is now the world’s oldest working planetarium! If you ever visit the Netherlands, it is definitely worth to take a trip to Franeker and see Eise’s Planetarium.

Special Event

This month's special events are the Venus/Jupiter conjunction and the Leonid meteor shower.

The morning of November 5th should be a real treat. For months Jupiter and Venus have been traveling towards each other (that is called their appulse), and now they will reach conjunction: their closest apparent approach. The dazzling pair of Venus and Jupiter will rise about three hours before the Sun. The two should be a little further apart than your finger held at arm’s length. Try viewing with a pair of binoculars or a telescope with a low power lens. You should be able to see both of these beauties together through the eyepiece. But also with the naked eye, this will appear quite spectacular. The two will actually appear closest (reach conjunction) when they are still below the horizon on the evening of the 4th.

The Leonid meteor shower reaches its peak on the morning of the 17th. They seem to originate from the constellation Leo, hence their name. Their true source is the comet Temple-Tuttle, which orbits the Sun about every 33 years. When a comet gets close to the sun, millions of tiny particles are thrown from the comet, thus creating a big path of these particles. The Earth’s orbit happens to pass through a small part of this path. When one of these particles (usually no bigger than a small grain of sand) enters the Earth’s atmosphere, it burns up. Because the Leonids are moving at such a high speed in relation to Earth, a number of these meteors leave a long vapor trail. Comet Temple-Tuttle was nearest the Sun in 1998. The following four years were quite spectacular for viewing the Leonids. People were seeing thousands of meteors within an hour’s time. This year we should expect anywhere from 15 – 100 meteors per hour, which is still quite impressive.

Talking about the comet Temple-Tuttle; NASA has planned a mission to this comet, and not just to take pictures! The mission is called ‘Deep Impact’ and they actually plan to slam a spacecraft into the comet to see what will happen to it, and to learn more about the structure of comets. For more information on Deep Impact, you can visit the official Deep Impact website. NASA hopes to launch Deep Impact in January 2005.

October 2004

Long ago, people thought that an eclipse of the Sun or the Moon had a specific meaning. Of course, no one understood exactly what was happening when the Sun suddenly disappeared, and people were fearful, thinking that it was caused by an angry god.

The first person to successfully predict a solar eclipse was the Greek philosopher Thales, who predicted the solar eclipse of May 585 BC! This is quite amazing, because Thales did not have a computer or calculator more than 2500 years ago.

Today, of course, we understand how the planets and their moons move and interact in our Solar System, and we can predict and calculate any eclipse with great precision.

Solar eclipses occur in patterns or 'Eclipse Seasons', which are periods when an eclipse (or many eclipses) are possible. This is the way Astronomers can calculate that it is possible to have up to 5 (!) solar eclipses in one year, as happened in 1935.

Here is another interesting fact: if there is a total lunar eclipse, this always is accompanied by a solar eclipse! This October is no exception: although invisible from Austin, people in Alaska will see a partial solar eclipse this month.

Special Event

This month's special events are the Orionids but the real showpiece is the
total lunar Eclipse.

The Orionids are, just like the Perseids in August, an annual meteor shower. Although the Orionids are normally less spectacular then the Perseids, there is always a chance of seeing something amazing. The Orionids seem to emanate from just north of the constellation of Orion. The maximum activity of probably around 15 shooting stars per hour will occur after midnight around October 22-nd. For further instructions on observing the Orionids, please check the information on the Perseids, which is described in the August edition of AstroNews.

On October 27, we're in for a treat! The only spoiler could be clouds, but other than that, a total lunar eclipse is even clearly visible from downtown. There are two kinds of eclipses: a solar eclipse, where the Moon is in between the Sun and the Earth, and a lunar eclipse, where the Earth is in between the Sun and the Moon (see graphic below).

A schematic representation of a lunar Eclipse and a solar eclipse. The Earth is represented by the blue circle, the Moon is the orange circle and the Sun the yellow circle. This image is not to scale.

Solar eclipses are very rare and incredibly spectacular if you are at the right place at the right time. They are so rare, that we will have to wait until the year 2017 until we see one again over the continental United States. But when you have the opportunity, you truly should make an effort to see it, because it is an unforgettable experience. However, although spectacular, they are very short-lived: in the matter of 2 or 3 minutes the Sun becomes visible again and the effect is ruined.

Lunar eclipses however, are more common. There are several reasons for this; firstly, the earth is much bigger and therefore has a larger shadow for the Moon to travel through. Secondly, with a solar eclipse, the shadow must pass over you in order to see the eclipse, and then only the observer can see this. But for a lunar eclipse you see the effect of earth's shadow on the Moon, so everyone who can see the Moon can see the eclipse! Because of all this, a lunar eclipse also lasts much longer than a solar eclipse; more than an hour instead of minutes.

Around 8 p.m., we can start to see the first effects when the Moon starts to travel into the Earth's shadow. The start of the eclipse is when the Moon reaches the penumbra (partial shadow), which is the light-gray colored region in the graphic above. You will even be able to see that the shadow on the Moon is curved and not a straight line, because the earth is a sphere. The second phase is when the Moon reaches the umbra or full shadow region. When the whole Moon is in the umbra, we have totality. The Moon will be a wonderful spooky reddish color for over an hour; what a nice treat right before Halloween!. Then the Moon will touch the penumbra again, and slowly travel out of the Earth's shadow completely, until we have 'just' a normal full moon again at about 12:30 a.m.

Observing the eclipse is very easy: just take a chair to your yard and enjoy. The Moon will still be rather low on the horizon at 7 p.m., but will gradually move higher. Simple binoculars or a small telescope may enhance the experience but are not needed. Because we are looking at the Moon, observing is completely safe. You do not have to take any precautions as would be needed if viewing a solar eclipse. Just don't forget to blink when you are awed by Mother Nature!

September 2004

Of course you know that the sun rises in the East and sets in the West, but not only sun does that also the moon rises in the East and sets in the west. In addition the planets do exactly the same! Almost all the objects from our solar system make the same apparent path through the sky: from East to West. The reason for this is that our solar system is flat, all the planets rotate in a disk (or a plane) around the sun and all the planets rotate in the same direction.

A representation of the ecliptic and the apparent path of the sun

The path that the planets and the moon follow is called the ecliptic. The moon nearly follows this path as well, but strays above and below it in the time (almost a month) it takes to go around the earth once. During this time, the moon crosses the ecliptic twice. From the Greek word for ‘failure to show up’ an eclipse happens when the sun, moon and earth form a straight line as the moon crosses the ecliptic. If the order of the line is sun-moon-earth, we have an eclipse of the sun – or solar eclipse. This is when the moon’s shadow is on the earth. If the sun-earth-moon line up, we have a lunar eclipse – the earth’s shadow is cast onto the moon. With either of these situations, a full or partial shadow is present. If the alignment is exact, then we have a total eclipse.

As you may know, the earth is tilted on its axis (about 23.5°) in relation to its path around the sun. The angle of tilt can be seen on most globe atlases of earth. This tilt defines how big the Arctic and Antarctic Circle is at each end of our planet. Each region is tilted away from the sun for six months and tilted toward it the following six months. This, of course, is the reason each polar region has half year of light (i.e. the ‘Land of the Midnight Sun’) and a half year of darkness. The autumnal equinox marks the first day the sun shines at the South Pole, and the beginning of six months of darkness at the North Pole.

August, 2004

As you have undoubtedly heard the current mission to Saturn is called The Cassini-Huygens Mission. The name Cassini is in honor of the Italian/French astronomer Giavanni Dominico Cassini. He was born June 8, 1625 in Nice, Italy and died at the respectable age of 87 (in 1712 in Paris, France).

As was more common in those days, Cassini was much more than just an astronomer. He wrote papers on hydraulic engineering, was an inspector of water and waterways, and was also the superintendent of the improvements to a castle! We remember him mostly for the discoveries he made as an astronomer.

Cassini, together with his colleague Jean Richer, was the first to actually calculate the distance to the planet Mars. This told them something about the size of our solar system. This was a very important discovery! Back then nobody knew how far away from Earth (or each other) the planets were, let alone the size of the Universe. Likewise, in Cassini's day, there were discussions about whether the Earth was flat and whether or not the Earth rotated. He was the first to observe and measure rotation of other planets. Because all the other planets rotated, Cassini speculated that the Earth rotates as well. Why would the Earth be any different?

He also discovered four moons around Saturn (Tethys, Dione, Rhea and Iapetus), (co-) discovered Jupiter's red spot and was the first to observe the large gap in the rings of Saturn, which we call the Cassini division. Wow, what an amazing person he must have been!

For more information on the Cassini-Huygens mission to Saturn go to the NASA Mission home page.

Special Event

This month's special events are related: the Autumnal Equinox and the Harvest Moon.

The Autumnal equinox marks the beginning of fall in central Texas and the rest of the northern hemisphere. At this point we can officially begin anticipating cooler weather :-). On both equinoxes (there is one for spring as well) night and day are equal. In fact, the word equinox comes from Latin, meaning ‘equal night.’ After the autumnal equinox, nights become longer and days become shorter all the way until the winter solstice in December. Equivalently, days become longer with the advent of the Vernal (spring) equinox. These events are opposite for the southern hemisphere.

The Harvest Moon is just the name we give to the full moon closest to the autumnal equinox. As with every full moon, the harvest moon rises right at sunset. During the year – on average – the moon rises 50 minutes later each evening. The harvest moon rises only about 25 minutes earlier each night for several nights, thus keeping after twilight darkness at bay for at least an extra week while the moon is fat. This was important to farmers gathering crops in the many centuries before electricity. These days it helps us forget – for a little while – that the days are truly getting shorter. The reason the Harvest Moon rises just 25 minutes later each night is because the moon’s path is closest to the ecliptic (see the Did You Know section below) at this time of year.

August 2004

Special Event

This month's special event is the Perseid Meteor shower. Peak viewing is on the night of August 12th into the morning of the 13th. The Perseids are remnants from the comet Swift-Tuttle and are named for the constellation Perseus. Just like train tracks seem to come together at the horizon, 'shooting stars' of a meteor shower also seem to originate from a single point. In this case, they seem to emanate from the stars that make up the constellation Perseus.

Meteors are small pieces of rock and dirt varying in size from tiny dust particles to sand grains with an occasional pebble thrown into the mix. When a comet travels through our solar system, the sun heats the comet causing some evaporation. The comet leaves behind a dust trail. When the earth's orbit travels through such a trail, the dust hits our atmosphere at a great speed causing it to burn up. Often, these meteor showers are recurrent and predictable to a certain degree. The Perseid meteor shower is an annual event but the intensity of this year's shower (how many shooting stars per hour) is uncertain. Under a dark sky, 60 - 100 per hour is typical for this shower. However, there are indications this year's Perseids might be a lot better (say 300 an hour) or spectacular like a 1000 or more per hour!

The moon cooperates nicely this year for the Perseid Meteor shower - by being mostly absent. If the sky is clear and you are away from city lights, conditions should be ideal for observing. The darker the spot you can find the better. Also, make certain you have a clear view of (especially) the North-North Eastern sky. Unfortunately, for most, the best time to observe meteor showers is very early in the morning with the peak around 3 a.m. We might get lucky this year and see a terrific show at around 11 p.m.

Good luck viewing - and if you see a falling star, please wish for a planetarium!

For more information on the Perseid Meteor shower you can read the article from Sky & Telescope magazine.